Synthesis and characterization of mono S-lipidated peptide hydrogels: a platform for the preparation of reactive oxygen species responsive materials.

In this work we report the synthesis of mono lipidated peptides containing a 3-mercaptopropionate linker in the N-terminus by means of a photoinitiated thiol-ene reaction (S-lipidation). We evaluate the self-assembling and hydrogelation properties of a library of mono S-lipidated peptides containing lipid chains of various lengths and demonstrate that hydrogelation was driven by a balance between the lipid chain's hydrophobicity and the peptide's facial hydrophobicity. We further postulate that a simple calculation using estimated values of log D could be used as a predictor of hydrogelation when designing similar systems. A mono S-lipidated peptide containing a short lipid chain that formed hydrogels was fully characterized and a mechanism for the peptide hydrogelation developed. Finally, we demonstrate that the presence of the thioether group in the mono S-lipidated peptide hydrogels, which is a feature lacking in conventional N-acyl lipidated systems, enables the controlled disassembly of the gel via oxidation to the sulfoxide by reactive oxygen species in accordance with a hydrophobicity-modulated strategy. Thus, we conclude that mono S-lipidated peptide hydrogels constitute a novel and simple tool for the development of tissue engineering and targeted drug delivery applications of diseases with overexpression of reactive oxygen species (e.g. degenerative and metabolic diseases, and cancers).

Nanoribbon self-assembly and hydrogel formation from an NOctanoyl octapeptide derived from the antiparallel ß-Interface of a protein homotetramer.

The effect of installing different lipid chains (C6, C8, C10, and C16) on the N-terminus of an octapeptide derived from the antiparallel ß-interface of the diaminopimelate decarboxylase protein homotetramer has been investigated. Notably, the C8 peptide conjugate assembled into wide twisted nanoribbons and formed hydrogels, which to the best of our knowledge constitutes the first example of a peptide containing an eight carbon alkyl chain that demonstrates these properties, a space typically occupied by peptide amphiphiles with long lipid chains. Furthermore, this self-assembling lipopeptide exhibited pH and temperature stability with shear thinning properties suitable for biomedical applications. Importantly, in this work the application of the polystyrene-based sorbent Diaion™ HP20SS for the simple large-scale purification of self-assembling peptides is presented as an alternative to the use of time-consuming and labor-intensive reverse-phase high-performance liquid chromatography. STATEMENT OF SIGNIFICANCE: Peptides that can self-assemble into defined nanostructures are highly attractive for many biomedical applications given their unique physical and chemical properties. It is recognized that self-assembling peptides derived from naturally occurring proteins offer an unlimited source of functionalities and structures, which are hard to uncover with designed sequences. In this study, we have investigated the effect of installing different lipids chains on the N-terminus of an octapeptide derived from the antiparallel ß-interface of the diaminopimelate decarboxylase protein homo tetramer. We also reported the use of polymeric DiaionⓇ HP20SS beads as an alternative solid support to purify self-assembling peptides.

Directed self-assembly of peptide-diketopyrrolopyrrole conjugates - a platform for bio-organic thin film preparation.

Increased water solubility and long-range intermolecular ordering have been introduced into the fluorescent organic molecule thiophene-diketopyrrolopyrrole (TDPP) via its conjugation to the octapeptide HEFISTAH, which is derived from the protein-protein ß-interface of the homo-tetramer protein diaminopimelate decarboxylase. The octapeptide, and its TDPP mono- and cross-linked conjugates were synthesised using 9-fluorenylmethoxycarbonyl (Fmoc) based solid-phase peptide synthesis (SPPS). Unlike the unmodified peptide, the resulting mono-linked and cross-linked peptides showed a fibrous morphology and formed hydrogels at 4 wt% in water at neutral pH, but failed to assemble at pH 2 and pH 9. Further peptide characterization showed that the TDPP organic core enhances peptide self-assembly and that both peptides assembled into fibers with a parallel ß-sheet structure. Furthermore, UV-vis spectroscopic analysis suggests that the TDPP molecules form H-type aggregates where the chromophores are likely to be co-facially packed, but rotationally and/or laterally offset from one another. This intermolecular coupling indicates that π-π stacking interactions are highly likely - a favourable sign for charge transport. The enhanced aqueous solubility and self-assembling properties of the TDPP-peptide conjugates allowed the successful preparation of thin films. Atomic force microscopy, X-ray diffraction and UV-vis spectroscopic analysis of these thin films revealed that the hybrid materials retained a fibrous morphology, ß-sheet structures and strong intermolecular coupling between neighbouring TDPP molecules. These results open an exciting avenue for bio-organic materials development, through structural and electronic tuning of the TDPP core.